U.S. patent number 7,283,789 [Application Number 10/527,923] was granted by the patent office on 2007-10-16 for apparatus and method for transmitting wireless data using an adaptive frequency selection.
This patent grant is currently assigned to Open Solution Co., Ltd.. Invention is credited to Suk-whan Choi.
United States Patent |
7,283,789 |
Choi |
October 16, 2007 |
Apparatus and method for transmitting wireless data using an
adaptive frequency selection
Abstract
Disclosed is a method and device for locally transmitting
digital wireless data through a searched channel with no
interference. Firstly, data is transmitted and received through a
setup channel. A channel having a different frequency from the
setup channel is set as a temporary replacement channel. Data is
transmitted and received through the temporary replacement channel,
and it is checked whether there is channel interference. When there
is no channel interference, the temporary replacement channel
information is stored, and data is transmitted and received after
returning to the setup channel. When it is detected that channel
interference continuously occurs while transmitting and receiving
data through the setup channel, data is transmitted and received
after changing the stored replacement channel to a new setup
channel.
Inventors: |
Choi; Suk-whan (Uiwang-si,
KR) |
Assignee: |
Open Solution Co., Ltd.
(KR)
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Family
ID: |
31987449 |
Appl.
No.: |
10/527,923 |
Filed: |
November 14, 2002 |
PCT
Filed: |
November 14, 2002 |
PCT No.: |
PCT/KR02/02123 |
371(c)(1),(2),(4) Date: |
March 16, 2005 |
PCT
Pub. No.: |
WO2004/025864 |
PCT
Pub. Date: |
March 25, 2004 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20050272434 A1 |
Dec 8, 2005 |
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Foreign Application Priority Data
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Sep 16, 2002 [KR] |
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10-2002-0056181 |
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Current U.S.
Class: |
455/63.3;
455/63.1; 370/437; 375/E1.036 |
Current CPC
Class: |
H04B
1/715 (20130101); H04B 2001/7154 (20130101) |
Current International
Class: |
H04B
1/00 (20060101); H04B 15/00 (20060101) |
Field of
Search: |
;455/450,63.1,63.3
;370/329,437 ;375/132 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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7-297761 |
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Nov 1995 |
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JP |
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2002-246961 |
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Aug 2002 |
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JP |
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Other References
PCT International Search Report; International application No.
PCT/KR02/02123; International filing date: Nov. 14, 2002; Date of
Mailing: Jun. 17, 2003. cited by other .
PCT International Preliminary Examination Report; International
application No. PCT/KR2002/002123; International filing date: Nov.
14, 2002; Date of Completion: Jan. 20, 2005. cited by
other.
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Primary Examiner: Orgad; Edan
Assistant Examiner: Guzman; April S.
Attorney, Agent or Firm: Cantor Colburn LLP
Claims
The invention claimed is:
1. A method for transmitting wireless data using an adaptive
frequency selection, the method being used in a device which
includes a master and a slave and locally transmits wireless data
in a frequency-changeable manner, the method comprising the steps
of: setting up a setup channel for data transmission; the master
and the slave transmitting data through the setup channel at a
first channel frequency; checking whether there is channel
interference in the setup channel; checking whether a replacement
channel is stored if channel interference within a recoverable
range occurs within the setup channel; where no replacement channel
is stored, setting a channel having a second frequency different
from the first frequency as a temporary replacement channel; and
requesting the slave to change the first channel frequency to the
second channel frequency; transmitting data through the temporary
replacement channel if a response to the request for changing
channel frequencies is received from the slave; storing the
temporary replacement channel as a replacement channel if there is
no channel interference in the temporary replacement channel;
checking whether there is interference in the replacement channel
and the setup channel while alternately transmitting data through
the setup channel and the replacement channels; and when there is
continuous channel interference in the setup channel, transmitting
data after changing the stored replacement data to a new setup
channel.
2. The method as set forth in claim 1, further comprising the step
of: when there is continuous interference in the replacement
channel, discarding the stored replacement channel information, and
finding and storing a new replacement channel with no
interference.
3. The method as set forth in claim 1, wherein the slave reports to
the master information on whether channel interference occurs while
transmitting data through the stored replacement channel.
4. The method as set forth in claim 3, wherein the check on whether
there is channel interference is performed based on whether access
codes inserted in transmitted and received packets are
identical.
5. The method as set forth in claim 3, wherein the check on whether
there is channel interference is performed based on the number of
RS-decoder bit errors of real-time data inserted in a received
packet, or based on the number of bit errors of non-real-time data
known to the master and slave.
6. The method as set forth in claim 4, wherein a check on whether
the channel interference continuously occur is performed by
comparing the accumulated number of the bit errors of the real-time
data and non-real-time data or the accumulated number of the
non-identical bits of the access codes for a predetermined period
of time with a corresponding prestored threshold value.
7. The method as set forth in claim 1, wherein a length of data
transmission period through the replacement channel is set to a
length in which it is possible for the slave to recover loss of
data transmitted through the replacement channel by obtaining and
deinterleaving both data received before changing to the
replacement channel and data received after returning to the setup
channel.
8. A method for transmitting wireless data using an adaptive
frequency selection, the method being used in a device which
includes a master and a slave and locally transmits wireless data
in a frequency-changeable manner, the method comprising the steps
of: a first step of transmitting and receiving data through a setup
channel; a second step of checking whether there is channel
interference in the setup channel; a third step of when the channel
interference within a recoverable range occurs in the setup
channel, checking whether a replacement channel is stored; a fourth
step of when the replacement channel is not stored, setting a
channel, which has a different frequency from the setup channel, as
a temporary replacement channel, and then checking whether there is
channel interference while transmitting and receiving data; a fifth
step of, when there is no channel interference, storing the
temporary replacement channel as a replacement channel and then
returning to the setup channel; a sixth step of checking whether
there is interference in the setup channel and the stored
replacement channel while alternately transmitting data through the
setup channel and the stored replacement channel; and a seventh
step of when there is channel interference in the stored
replacement channel, discarding stored replacement channel
information and returning to the first step; and an eighth step of,
when interference continuously occurs in the setup channel,
transmitting data after changing the stored replacement channel to
a new setup channel.
9. A device for transmitting wireless data through an adaptive
frequency selection by using a frequency hopping scheme, the device
comprising: a transmission data generator for appending at least a
redundancy and CRC for error recovery to data to be transmitted,
and interleaving and outputting the resulting data; an access code
generator for appending an access code to the outputted
transmission data, and packetizing the resulting data; an access
code detector for detecting an access code from a received packet;
a received data restoration unit for checking a CRC in data of the
received packet to determine whether an error occurs in the data,
and then RS-decoding deinterleaved data to recover a data loss, the
device further comprising: a channel interference detector for
comparing the accumulated number of non-identical bits of access
codes detected for a predetermined period of time with a prestored
threshold value, and detecting from the comparison result whether
channel interference occurs; a hopping frequency generator for
generating random hopping frequencies in response to a device
address and a clock inputted thereto; and a transmission/reception
controller for searching channels of the random hopping frequencies
for one channel with no interference, storing the searched channel
as a replacement channels if channel interference within a
recoverable range occurs in the setup channel, and then changing
the replacement channel to a new setup channel or searching for a
new replacement channel and storing the searched replacement
channel if interference is continuously detected by the channel
interference detector while alternately transmitting data through
the setup channel and the replacement channel.
10. The device as set forth in claim 9, wherein the channel
interference detector detects whether channel interference occurs
by accumulating the number of data bit errors of the received
packet and then comparing the accumulated number of data bit errors
with another threshold value.
11. The device as set forth in claim 9, wherein the
transmission/reception controller includes an internal memory
storing program data for searching for a channel with no
interference, the program data allowing the device to sequentially
perform the steps of: requesting a slave to perform a corresponding
process for allowing data transmission and reception through one of
the random hopping frequencies generated from the hopping frequency
generator; transmitting/receiving data through the requested
channel frequency; and storing the hopping frequency as information
of the replacement channel when there is no channel
interference.
12. The method as set forth in claim 2, wherein the slave reports
to the master information on whether channel interference occurs
while transmitting data through the stored replacement channel.
13. The method as set forth in claim 5, wherein a check on whether
the channel interference continuously occur is performed by
comparing the accumulated number of the bit errors of the real-time
data and non-real-time data or the accumulated number of the
non-identical bits of the access codes for a predetermined period
of time with a corresponding prestored threshold value.
14. The method as set forth in claim 2, wherein a length of data
transmission period through the replacement channel is set to a
length in which it is possible for the slave to recover loss of
data transmitted through the replacement channel by obtaining and
deinterleaving both data received before changing to the
replacement channel and data received after returning to the setup
channel.
Description
TECHNICAL FIELD
The present invention relates to a local-area wireless data
transmission system, and more particularly to a method and
apparatus for finding a channel frequency with no interference and
transmitting real-time wireless data at the found channel
frequency.
BACKGROUND ART
Bluetooth and wireless local area network (LAN) techniques using a
2.4 GHz industrial scientific medical (ISM) frequency band
generally employ spread spectrum methods such as a frequency
hopping spread spectrum (FHSS) method and a direct sequence spread
spectrum (DSSS) method.
The DSSS method is adapted to obtain a spread signal by multiplying
data by a spread code, and the FHSS method is adapted to shift a
frequency band according to a spread code. In particular, the FHSS
method transmits a signal to be spread while hopping its carrier
frequencies at intervals of a predetermined time according to a
hopping pattern, and converts a narrowband signal into a wideband
signal over a time average. This FHSS method generates a random
hopping pattern in an ISM band suitable to the standard of each
country and transmits data at a frequency based on the generated
pattern, resulting in the advantages of minimizing frequency
overlap, reducing losses by a multipath owing to fast frequency
conversion and being simple in construction. As a result, at the
present, the FHSS method is widely used in low-price-type wireless
devices (for example, Bluetooth devices).
However, the FHSS method has a disadvantage in that the hopping is
performed irrespective of the presence or absence of an
interference source over the entire frequency band, resulting in
occurrence of a packet loss when the hopping is made to a specific
frequency where interference is present. In this case, data (voice,
audio and video) to be transmitted in real time cannot help
suffering a degradation in quality if no error recovery is
made.
DISCLOSURE OF THE INVENTION
Therefore, the present invention has been made in view of the above
problems, and it is an object of the present invention to provide a
method and apparatus for adaptively finding a channel frequency
with no interference and transmitting wireless data at the found
channel frequency, so that the quality of wireless transmission of
real-time data can be enhanced by recovering a data loss resulting
from intermittent interference and avoiding the influence of
continuous interference.
In accordance with one aspect of the present invention, the above
and other objects can be accomplished by the provision of a device
for transmitting wireless data through an adaptive frequency
selection by using a frequency hopping scheme, the device
comprising:
a transmission data generator for appending at least a redundancy
and CRC for error recovery to data to be transmitted, and
interleaving and outputting the resulting data;
an access code generator for appending an access code to the
outputted transmission data, and packetizing the resulting
data;
an access code detector for detecting an access code from a
received packet;
a received data restoration unit for checking a CRC in data of the
received packet to determine whether an error occurs in the data,
and then RS-decoding deinterleaved data to recover a data loss,
the device further comprising:
a channel interference detector for comparing the accumulated
number of non-identical bits of access codes detected for a
predetermined period of time with a prestored threshold value, and
detecting from the comparison result whether channel interference
occurs;
a hopping frequency generator for generating random hopping
frequencies in response to a device address and a clock inputted
thereto; and
a transmission/reception controller for searching channels of the
random hopping frequencies for one channel with no interference,
storing the searched channel as a replacement channel, and, if
interference is continuously detected by the channel interference
detector while alternately transmitting data through the setup
channel and the replacement channel, and then changing the
replacement channel to a new setup channel or searching for a new
replacement channel and storing the searched replacement
channel.
Preferably, the transmission/reception controller includes an
internal memory storing program data for searching for a channel
with no interference, the program data allowing the device to
sequentially perform the steps of:
requesting a slave to perform a corresponding process for allowing
data transmission and reception through one of the random hopping
frequencies generated from the hopping frequency generator;
transmitting/receiving data through the requested channel
frequency; and
storing the hopping frequency as information of the replacement
channel when there is no channel interference.
In accordance with another aspect of the present invention, there
is provided a method for transmitting wireless data using an
adaptive frequency selection, the method being used in a device
which includes a master and a slave and locally transmits wireless
data in a frequency-changeable manner, the method comprising the
steps of:
finding and storing a replacement channel with no interference
which has a different frequency from a setup channel set as a data
transmission channel;
checking whether there is interference in the replacement and setup
channels while alternately transmitting data through the setup and
replacement channels; and
when there is continuous channel interference in the setup channel,
transmitting data after changing the stored replacement data to a
new setup channel.
According to the present invention, a replacement channel with no
interference is found and stored in advance. Thus, when channel
interference continuously occurs, the stored replacement channel
can be changed to a new setup channel for data transmission,
thereby minimizing a data loss.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects, features and other advantages of the
present invention will be more clearly understood from the
following detailed description taken in conjunction with the
accompanying drawings, in which:
FIG. 1 is a block diagram showing the construction of a wireless
data transmission apparatus in accordance with a preferred
embodiment of the present invention;
FIG. 2 is a view illustrating the structures of packets transmitted
and received by the wireless data transmission apparatus in
accordance with the embodiment of the present invention;
FIG. 3 is a flow chart illustrating the entire procedure of
changing a current channel to a channel with no interference in
accordance with the embodiment of the present invention;
FIG. 4 is a flow chart illustrating the step in FIG. 3 of searching
for a replacement channel with no interference; and
FIG. 5 is a view supplementarily illustrating the step in FIG. 3 of
periodically checking whether a replacement channel is subject to
interference.
BEST MODE FOR CARRYING OUT THE INVENTION
Now, preferred embodiments of the present invention will be
described in detail with reference to the annexed drawings. In the
following description, a detailed description of known functions
and configurations incorporated herein will be omitted when it may
make the subject matter of the present invention rather
unclear.
FIG. 1 is a block diagram showing the construction of a wireless
data transmission apparatus in accordance with a preferred
embodiment of the present invention, and FIG. 2 is a view
illustrating the structures of packets transmitted and received by
the wireless data transmission apparatus in accordance with the
embodiment of the present invention. For reference, the wireless
data transmission apparatus according to the embodiment of the
present invention may be used as, for example, a wireless
transmitter or wireless receiver for a surround speaker. In this
case, an optical (CD/DVD) pickup reproduction device will be
disposed around the wireless transmitter. The wireless transmitter
according to the embodiment of the present invention will receive
real-time data R/L SURROUND from a decoder AC-3, which processes a
signal reproduced from an optical medium, packetize the received
data by components, which will be described later, and wirelessly
transmit the resulting packet through a Bluetooth radio frequency
(RF) transmitter/receiver module at a short distance. Then, the
wireless receiver, which is constructed as shown in FIG. 1, will
receive and process the transmitted packet, so that audio sound
reproduced from the optical medium can be outputted through the
speaker.
A description will hereinafter be given of the construction of the
wireless data transmission apparatus in accordance with the
embodiment of the present invention with reference to FIG. 1. The
wireless data transmission apparatus basically comprises a
transmitting data generation unit A, an access code generator 14,
an access code detector 22, a received data restoration unit B, a
hopping frequency generator 48, a channel interference detector 46,
and a transmission/reception controller 16. The wireless data
transmission apparatus further comprises a modem 18 and an RF
transmitter/receiver module 20, as in a general local-area wireless
transmitter.
The transmitting data generation unit A acts to append at least a
redundancy and CRC (Cyclic Redundancy Check (Code)) for error
recovery to data to be transmitted, and interleave and output the
resulting data. To this end, the transmitting data generation unit
A includes, as shown in FIG. 1, a compressor 30 for compressing
real-time data, a scrambler 32 for scrambling the real-time data
compressed by the compressor 30, and a Reed-Solomon (RS) encoder
34. The RS encoder 34 functions to append a redundancy for error
recovery to output data from the scrambler 32. The appended
redundancy is used in an RS decoder 40 to be described later. An
interleaver 36 is connected to the output of the RS encoder 34 to
interleave the redundancy-appended real-time data to prevent a
burst error from occurring in transmission.
A CRC generator 10 is provided in the transmitting data generation
unit A to generate a CRC of a predetermined number of bits from
non-real-time data (for example, volume control data) and append
the generated CRC to a data block. A whitening & 1/3 forward
error correction (FEC) encoder 12 is also provided in the
transmitting data generation unit A to adjust a direct current (DC)
offset for the CRC-appended data block and repeatedly output input
data 3 bits by 3 bits to minimize an error possibility on a
channel.
The access code generator 14 is connected to the output of the
transmitting data generation unit A to append an access code to
data to be transmitted, generated by the generation unit A, and
packetize the resulting data. The resulting packet has a structure
as shown in FIG. 2. Namely, when the subject is a master, a forward
packet transmitted from the master includes an access code,
non-real-time data and real-time data, and a backward packet
transmitted from a slave includes an access code and non-real-time
data. A data packet appended with an access code by the access code
generator 14 is transmitted to a different wireless data
transmission apparatus as the slave through the
transmission/reception controller 16, modem 18 and RF
transmitter/receiver module 20.
On the other hand, a data packet is received by the RF
transmitter/receiver module 20, demodulated by the modem 18 and
then inputted to the access code detector 22. The access code
detector 22 detects an access code from the received packet and
provides the detected access code to the channel interference
detector 46 to be described later, so that it can be used for
checking whether channel interference is present.
The received data restoration unit B acts to check a CRC in data of
the received packet to determine whether an error has occurred in
the data, and RS-decode deinterleaved data to recover a data loss.
That is, in the received data restoration unit B, a deinterleaver
38 deinterleaves and outputs interleaved data, and the RS decoder
40 recovers the data packet from a loss using a redundancy
contained in the deinterleaved data. The RS decoder 40 also acts to
output the number of irrecoverable bit errors to the channel
interference detector 46. A descrambler 42 descrambles scrambled
real-time data, and a decompressor 44 decompresses and outputs the
descrambled data.
A dewhitening & 1/3 FEC decoder 24 is also provided in the
received data restoration unit B to perform a 1/3 rate FEC decoding
operation to process non-real-time data. This 1/3 rate FEC decoding
operation is performed by carrying out a majority decision (select
a major binary value of 3-bit binary data) for the received packet
data on a 3 bits basis. As being subjected to the 1/3 rate FEC
decoding operation, the packet data is reduced to 1/3 in size. The
resulting packet data is inputted to a dewhitening block, which
then dewhites the inputted data on the basis of the same whitening
seed value as that in the transmitter. After being subjected to the
FEC decoding operation and dewhitening operation, the packet data
is finally inputted to a CRC checker 26. The CRC checker 26 acts to
check a CRC in the inputted packet data to determine whether an
error is present in that packet data.
The channel interference detector 46 acts to accumulate the number
of non-identical bits of access codes for a predetermined period of
time, compare the accumulated number with a prestored threshold
value, detect from the comparison result whether continuous channel
interference is present, and send the detection result to the
transmission/reception controller 16. Alternatively, the channel
interference detector 46 may accumulate the number of data bit
errors of the received packet provided from the RS decoder 40,
compare the accumulated number with another threshold value and
detect from the comparison result whether channel interference is
present.
The hopping frequency generator 48 acts to generate random hopping
frequencies in response to a device address and a clock inputted
thereto. The device address is shared by the data transmission
device and data reception device, and is not changed once being
initially set. The clock is transferred from the master to the
slave in the process of initialization and then counted up every
cycle.
The transmission/reception controller 16 acts to transmit and
receive data packets over a channel set up in the initialization
process or a setup channel with no interference. The
transmission/reception controller 16 is also adapted to search
channels of the random hopping frequencies for one channel with no
interference, store the searched channel as a replacement channel,
alternately transmit data over the setup channel and the
replacement channel, and, if continuous interference in the setup
channel is detected by the channel interference detector during the
data transmission, change the replacement channel to a new setup
channel or search for a new replacement channel. To this end, the
transmission/reception controller 16 includes a memory for storing
program data for the above operation. After storing the replacement
channel, the transmission/reception controller 16 discards hopping
frequencies generated from the hopping frequency generator 48.
Although all the blocks for processing real-time data and
non-real-time data have been disclosed, the circuit construction
may be modified suitably for use as the master and slave. For
example, provided that the present wireless data transmission
apparatus is used as the slave, the functional blocks for
generation of real-time data may be removed from the transmitting
data generation unit.
A description will hereinafter be given of the operation of the
local-area wireless data transmission apparatus with the
above-stated construction which searches for a channel with no
interference and changes a current channel to the searched
channel.
FIG. 3 is a flow chart illustrating the entire procedure of
changing a current channel to a channel with no interference in
accordance with the embodiment of the present invention, FIG. 4 is
a flow chart illustrating the step in FIG. 3 of searching for a
replacement channel with no interference, and FIG. 5 is a view
supplementarily illustrating the step in FIG. 3 of periodically
checking whether a replacement channel is subject to
interference.
With reference to FIG. 3, the local-area wireless data transmission
apparatuses, which are equipped respectively with, for example,
Bluetooth modules and correspond respectively to the master and
slave, each set up a channel frequency for data packet transmission
through a system initialization step (step 50). In the below
description, such a channel for data packet transmission will be
referred to as a "setup channel". If the setup of a channel for
packet transmission is completed, then the master and slave each
transmit data over the setup channel (step 52). During this data
transmission, the transmission/reception controller 16 checks
through the channel interference detector 46 whether interference
is present in the setup channel (step 54). The channel interference
can be classified into intermittent interference and continuous
interference. It should be noted that a data loss by the continuous
interference is not recoverable, whereas a data loss by the
intermittent interference is recoverable by the RS decoder. In this
regard, according to the present invention, the
transmission/reception controller 16 is programmed to make a
distinction between the continuous interference and the
intermittent interference and recover a data loss, or change a
current channel to a channel with no interference unless the data
loss is recoverable. For reference, the check on whether channel
interference is present can be made on the basis of the number of
bit errors of real-time data or non-real-time data inserted in a
received packet, or based on whether access codes inserted in
transmitted and received packets are coincident with each other. In
the case where an accumulated number of bit errors of real-time
data or non-real-time data for a predetermined period of time, or
an accumulated number of non-identical bits of access codes exceeds
a prestored corresponding threshold value, the channel interference
may be determined to be the continuous interference. In other
words, in the case where an accumulated number of bit errors of
real-time data or non-real-time data for a predetermined period of
time, or an accumulated number of non-identical bits of access
codes does not exceed a prestored corresponding threshold value,
since it is within a range in which the data can be recovered by
interleaving, it may be determined that channel interference does
not exist.
If no channel interference is determined to be present at the above
step 54, then the transmission/reception controller 16 proceeds to
step 58 to check whether a stored replacement channel is present.
This replacement channel signifies a new channel to which a channel
(setup channel) currently transmitting data is to be changed for
data transmission when it is subject to the continuous
interference. If a previously searched and stored replacement
channel is present, then the transmission/reception controller 16
moves to step 60 to check whether the current time has reached a
time to check whether interference is present in the replacement
channel. If such a replacement channel is not present, the
procedure moves to step 68.
On the other hand, in the case where channel interference is
present but it is intermittent, i.e., in the case where an
accumulated number of bit errors of real-time data or non-real-time
data for a predetermined period of time, or an accumulated number
of non-identical bits of access codes exceeds a prestored
corresponding threshold value, the procedure moves to step 56 for
data recovery. It is preferable to define such a predetermined
period of time to be a data period in which it is possible to
recover a data loss using a redundancy that the slave obtains by
deinterleaving data interleaved by and transmitted from the master.
In such a case where data recovery is possible even thought
intermittent interference is present, the transmittance/reception
controller 16 checks whether a replacement channel is present,
while leaving the current setup channel unchanged (i.e., without
channel change) (step 58). If there is no replacement channel, the
controller 16 moves to step 68 to search for the replacement
channel by the procedure of a subroutine shown in FIG. 4.
Hereinafter, the procedure until the replacement channel is
searched and stored is described referring to FIGS. 4 and 5.
Firstly, the transmission/reception controller 16 of the master
sets up a replacement channel frequency F2 in step 80. In this
case, it may be assumed that a channel frequency currently used for
data transmission is F1. In addition, it may be assumed that the
replacement channel frequency F2 to be newly set up is a temporary
replacement channel frequency. For the replacement channel
frequency F2, it is possible to use hopping frequencies randomly
generated from the hopping frequency generator 48. After setting
one of the hopping frequencies from the hopping frequency generator
48 as the temporary replacement channel frequency F2, the
transmission/reception controller 16 requests the slave to change
the current channel frequency to the channel frequency F2 in step
82. This request to change the channel frequency is performed
through the current setup channel of F1. Then, the slave of the
transmission/reception controller responds to the channel change
request in step 84. In this case that the setup channel of F1 is
changed to the temporary replacement channel of F2, the slave must
respond to the channel change request even when there are few
accumulated bit errors of the access code and the real-time data
that were received from the master through the setup channel of F1
until this time. This is for the following reasons. Even though the
real-time data is normally received until this time, i.e., before
changing to the replacement channel of F2, in the case where a data
loss occurs in the received data after changing to the replacement
channel of F2 and then the channel returns to the setup channel of
F1, there must be no data loss for a specific time after returning
to the setup channel of F1 in order to achieve the interleaving
effect and recover the data loss occurring during the period of the
replacement channel.
When the transmission/reception controller of the slave issue a
response to the channel change request, the transmission/reception
controller 16 of the master receives the response in step 86 and
then moves to step 88. In step 88, the transmission/reception
controllers 16 of both the master and slave change the channel to
the temporary replacement channel of F2 after storing the current
setup channel of F1, and then transmits data through the temporary
replacement channel of F2 in step 90.
As shown in case A of FIG. 5, in the case where the channel
frequency changes from F1 to F2 and then returns to F1, the slave
must respond to the channel change request as in step 82, provided
it is considered that it is possible to recover the data loss in
the frequency F2 by using data received through both the former and
latter frequencies F1. This is for the following reasons. There is
no problem when channel interference does not occur in the
frequency F2. However, if channel interference occurs in the
frequency F2, causing a data loss in the real-time data, it is
necessary to recover the data loss using both the received data
before changing to F2 and after returning to F1.
In step 90, each of the transmission/reception controllers 16 of
the master and the slave transmits data through the temporary
replacement channel of F2 during a predetermined period (i.e.,
replacement channel maintaining period), and then the controllers
move to step 92 to return to the frequency F1 and check whether
interference is present in the channel of F2. The check on whether
interference is present in the channel of F2 can be made on the
basis of the number of bit errors of real-time data or
non-real-time data, or based on whether access codes are coincident
with each other, as mentioned above. After checking whether there
is interference in the channel of F2, the transmission/reception
controller 16 of the slave reports the checked result to the master
in step 94.
In this case, in step 96, the transmission/reception controller 16
of the master determines whether interference is present in the
channel of F2, based on the checked result from the slave as well
as its own checked result. If it is determined that there is
interference in the channel of F2, the procedure returns to the
main routine as shown in FIG. 3, and the replacement channel search
process as mentioned above is performed again in the next super
frame period. Here, a super frame is defined as a set of a number
of data packets. If it is determined in step 96 that there is no
interference in the temporary replacement channel of F2, the
channel of F2 is stored in the internal memory as a normal
replacement channel with no interference in step 98, and then the
procedure returns to the main routine.
In other words, the replacement channel search is performed when
there is no stored replacement channel, and the method for
searching for the replacement channel is performed in such a manner
that, when the slave in the setup channel of F1 responds to the
channel change request in each super frame period, the channel is
changed to the temporary replacement channel of F2 and data is
transmitted through the channel of F2, and during the data
transmission in the channel of F2, it is checked whether there is
interference in the channel of F2 in order to search for a
replacement channel with no interference. The current setup channel
is continuously used when it is impossible to find the replacement
channel with no interference.
The remaining operation of the transmission/reception controller 16
is described referring to FIG. 3, after the replacement channel
information is stored in the controller.
If it is detected that there is intermittent interference or there
is no interference, while transmitting data through the setup
channel, the controller 16 moves to step 58 to check whether there
is a replacement channel. If the checked result is that the
replacement channel is found and stored by the method as shown in
FIG. 4, the controller 16 moves to step 60 to check whether the
current time has reached a time to check whether there is
interference in the replacement channel. This check time occurs
periodically at intervals of the super frame periods Sn, and the
super frame size depends on the interleaving size.
When the time comes to check whether there is interference in the
replacement channel (step 60) while data is transmitted through the
setup channel F1 in one super frame Sn, the controller 16 changes
the channel from the setup channel of F1 to the stored replacement
channel of F2 and transmits real-time data through the replacement
channel of F2. Then, the master and the slave check whether there
is interference in the replacement channel F2 in step 64. If there
is no such interference, the channel returns to the setup channel,
whereas, if there is interference, the channel returns to the setup
channel after discarding the replacement channel in step 66. That
is, according to the present invention, the check on whether there
is interference in the searched replacement channel is performed
periodically, specifically, by transmitting real-time data through
the replacement channel during a predetermined period (i.e.,
replacement channel maintaining period) in each super frame. If
there is interference in the replacement channel, the
transmission/reception controller 16 discards the stored
replacement channel in step 66 because there is no need to maintain
it, and returns to step 52. In this case, the replacement channel
search routine as shown in FIG. 4 is performed again because there
is no replacement channel. When it is determined that there is no
interference in the replacement channel in step 64, the controller
16 moves to step 52 and checks whether there is interference in the
setup channel of F1, while transmitting data again through the
setup channel F1.
Referring to FIG. 5, it is checked whether there is interference in
the setup channel and the replacement channel, alternately, in such
a manner that data is transmitted through the setup channel of F1
during a first period of each super frame (S1, S1, . . . ), and,
after the channel is changed to the replacement channel of F2 when
the time comes to check whether there is interference in the
replacement channel, data is transmitted through the replacement
channel of F2 during a second period of each super frame. In FIG.
5, "Case A" indicates the case where the setup channel of F1 is
used while monitoring the channel of F2. "Case B" indicates the
case where the setup channel of F1 is used while monitoring the
channel of F2 and, in addition, it is detected that there is
interference in the replacement channel of F2 while monitoring the
channel of F2, and then a new replacement channel is set to be
checked on its interference. For example, even though the checked
result in step 64 is that intermittent interference occurs in the
replacement channel, the replacement channel can be discarded,
provided that the intermittent interference continuously occurs
during a number of monitoring periods. This example is only an
optional feature.
In step 70, when a continuous monitoring of the stored replacement
channel of F2 results in a determination that there is no
interference in the channel of F2, and, in addition, there is
continuous interference in the channel of F1, the
transmission/reception 16 moves to step 74. In step 74, the
controller 16 transmits data after changing the stored replacement
channel F2 to a new setup channel. Of course, before this channel
change, it is necessary to request the slave to change the channel.
Upon receipt of a response to such a request,
transmission/reception controller 16 of the master communicates
real-time data with the slave through the replacement channel.
Thus, the master and slave can transmit data through the channel of
F2 with no interference. Until the data transmission is completed,
the controller 16 must check whether there is interference in the
setup channel in each super frame, and search for a new replacement
channel by the method as shown in FIG. 4. If a new replacement
channel of F3 is found, it is checked whether there is interference
in the channel of F2 while transmitting data through the channel of
F2, and then, at the end portion of the corresponding super frame,
it is checked whether there is interference in the found
replacement channel of F3 while transmitting data through the
replacement channel of F3. In such a manner, alternate interference
checks between the setup channel of F2 and the replacement channel
of F3 are repeatedly performed. Such a repeating procedure
corresponds to "Case C" of FIG. 5. In "Case C" of FIG. 5, because
interference occurs in the setup channel of F1, the channel is
changed to the replacement channel of F2 that has been monitored,
and thereafter a new replacement channel of F4 is monitored.
According to the present invention, after finding a replacement
channel with no interference, it is checked whether there is
interference in the setup channel and the replacement channel while
alternately transmitting data through the setup and replacement
channels in each super frame, as mentioned above. Therefore, even
through interference continuously occurs in the current setup
channel, the channel can be easily changed to the replacement
channel with no interference that has been monitored until this
time, thereby minimizing a data loss caused by channel
interference.
INDUSTRIAL APPLICABILITY
As apparent from the above description, in preparation for the case
where interference continuously occurs in the current setup
channel, a replacement channel frequency is searched and stored as
a preparatory channel in advance. Thus, the present invention has
an advantage in that, even though interference continuously occurs
in the current setup channel, the channel can be easily changed to
the stored replacement channel, thereby minimizing a real-time data
loss caused by continuous channel interference.
Although the preferred embodiments of the present invention have
been disclosed for illustrative purposes, those skilled in the art
will appreciate that various modifications, additions and
substitutions are possible, without departing from the scope and
spirit of the invention as disclosed in the accompanying
claims.
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